Superconductors.ORG (Joe Eck) claims the first observation of superconductivity above zero degrees Celsius. In repeated tests a small amount of the compound (Tl4Pb)Ba2MgCu8O13+ produced diamagnetic transitions over 277 Kelvin (see examples at page top) and resistive transitions over 276K (3C, 37F). This is the first time superconductivity has been seen above the freezing point of water. As such, once a refinement method is developed, this material could be successfully deployed in climates with year-round permafrost without any need for artificial cooling.
This milestone was achieved by substituting divalent lead (Pb II) into the barium (Ba) atomic sites that hole-dope the insulating layers of the 265K superconductor discovered in October 2010. Doping with Pb instead of Ba dampens lattice vibrations and further increases planar weight disparity along the C1 axis. Planar weight disparity has been found to be a key component of high temperature superconductivity. Since a minority phase also appeared near 271K magnetic, this makes the fourth and fifth world records that have resulted from a 9223 structure.
As with prior discoveries that are asymmetrical along the C axis, the volume fraction of (Tl4Pb)Ba2MgCu8O13+ is low (<1%). So commercialization will have to wait for a refinement method to be developed to increase the VF. As a result of a low VF, numerous R-T and magnetization tests may be necessary to see the respective transitions above the noise. This discovery is being released into the public domain without patent protection in order to encourage additional research. Synthesis was by the solid state reaction method. The chemical precursors were pelletized at 70,000 PSI and sintered for 35-36 hours at 865C. The pellet was then annealed for 10 hours at 500C in flowing O2. The magnetometer employed twin Honeywell SS94A1F Hall-effect sensors with a tandem sensitivity of 50 mv/gauss. The 4-point probe was bonded to the pellet with CW2400 silver epoxy and used 7 volts on the primary.
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